Strap sealers are well known and provide positive sealing action of overlapping courses of strap material. These sealers interlock overlapping courses of a strap into a high strength joint in a notch-type seal or a crimp seal. In notch-type sealers, jaws cut into the seal and the outer edges of the strap, turning tabs down (down notch) or up (reverse notch). In a crimp-type sealer, the edges of the strap and the seal are pressed together into wavy crimps especially shaped to produce maximum frictional forces on the strap.
Powered strap sealers are known. One type of powered sealer uses a pneumatic cylinder to actuate a pair of jaws that close onto the strap or the crimp seal. One such pneumatic sealer is disclosed in Crittenden, U.S. Pat. No. 6,422,272. While the pneumatic sealer functions well for creating strap seals, it requires a source of compressed air and thus, hoses to supply the air to the sealer. As such, its use is limited in that it cannot be easily moved around a work space, yard or the like.
A battery powered sealer is disclosed in Figiel, US Publication 2013/0085053. This sealer overcomes some of the drawbacks of known powered sealers in that it allows for remote use and is readily moved around a work space. However, as with any battery powered tool, the operating life of the tool between battery changes or charges, is related to the power required to form the seal and is limited by the battery capacity.
The joint is the weakest part of the strapping system, therefore the type of joining method used is very important if strength is an issue. The strength of a joint is defined as the force required to break the strap in uniaxial tension. This is then compared to the uniaxial strength of the strap and recorded as the percent difference (e.g., a sample of strap may have a 5,000 lb (2,300 kg) break strength and the seal may fail at 3,750 lbs. (1,750 kg), so the seal is said to have a 75% strength).
Single notch (two tabs, one on each side of the joint) joint strength is rated for a minimum of 45% of strap strength. Double notch (four tabs, two on each side of the joint) joint strength is rated for a minimum of 75% of strap strength. Illustrations of single notch 1 and double notch 2 joints are shown in FIGS. 1 and 2, respectively. Failure of single notch joints 1 is typically by pull through of the strap S from the joint 1. Failure of double notch joints is typically by pull through or strap S failure at the joint 1, 2. Pull though results when the strap S pulls though the seal tabs 3. Strap breakage occurs at the first weakest cross-section of the strap, for example, at the first notch. Double notch joints 2 require a balancing of distributing and holding the pulling force on the strap S against maintaining a minimum of 75% of the original cross-section of the strap S (and thus 75% strength).
Accordingly, there is a need for a powered sealing tool that operates through a sealing cycle so as to reduce the amount of power required to form the seal. Desirably, such a tool creates a seal that maintains a minimum of 75% of the original cross-section of the strap. More desirably, such a tool creates a double notch seal in a single operating cycle of the tool.